It seems like 80% of people I've heard talking about AoC are planning on doing it in Rust (including me!). It's definitely a great way to get up to speed with a language you're interested in learning.
I was proud last year when I got to day 18 with Python, but I'm setting the bar much lower this year. I don't have any experience with C/C++ (just C# and a bit of Go), so thinking more carefully about memory mgmt is new to me. But the functional aspects of Rust are pretty exciting.